Use of ad-blocking software has largely been a desktop issue, and while still costly, ad blocking has leveled off as publishers have asked or required visitors to disable their ad blockers in order to see content. On mobile, though, mobile ad blocking is creeping up.

Research from AudienceProject, a company that helps publishers understand online audiences, found that 8 percent of mobile sessions detected people using an ad blocker in the U.K., up from 2 percent in 2016. In the U.S., 5 percent of sessions were blocked, up from 2 percent in 2016. In Germany, which has ranked high in desktop ad-blocking use, 13 percent of sessions on mobile were blocked. (AudienceProject had no comparable figures for German.)

Across Dennis Publishing’s U.K. portfolio, mobile web ad-blocking rates have increased from 2 percent to 4 percent over the last 12 months, the company said. For France’s Le Monde, mobile ad blocking has shot up since January, with 20 percent of mobile sessions now blocked, which is close to its desktop rate, said Pierre Buffet, head of digital at Le Monde.

Publishers’ mobile sites typically aren’t as lucrative as desktop, but as people become increasingly mobile, there’s concern that ad blocking will take a bigger bite out of their mobile business as publishers can’t monetize those audiences with ads.

“We see mobile fill rates around between 60 percent and 80 percent; that’s not comparable to desktop,” said independent publishing consultant Oliver von Wersch. “Between 1 percent and 5 percent of blocked ads, this isn’t affecting the business in any way.”

Sean Blanchfield, CEO of PageFair, which sells ad-blocking solutions to publishers, noted that mobile ad blocking is growing, but from a small base.

Mobile ad-blocking rates have lagged desktop partly because blocking ads on mobile takes marginally more work on mobile, where you have to install an app or activate a browser plugin, than on desktop. Equally, publishers, wary of making the same ad overload mistakes they did on desktop, are actively managing the number of units, size, scale, format and position. Initiatives like the Coalition for Better Ads have also cleaned up the user experience on mobile.

Women Women Pleaser Women Pleaser Women Pleaser Pleaser Pleaser Pleaser Women Women Pleaser Women Women Pleaser Pleaser Growing concern over privacy infringements are spurring adoption of ad blocking, though, Blanchfield said. Data from App Annie in May found that downloads of the top five dedicated ad-blocking apps in the U.K. more than doubled in the past year to almost 70,000 times across Google Play and the iOS App Store combined.

“Of course it is a great threat for us, especially if it’s natively embedded on the browser,” said Bertrand Gié, digital director of France’s Le Figaro.

Another potential headwind for publishers will be the ePrivacy directive in Europe, requiring publishers to let consumers choose if they want to be tracked.

“Data-driven ad targeting on mobile is getting more difficult. If you’re not using data, you need different ways to measure audience and context. That’s more than putting an ad on the page with BT Sport,” said Simon Kvist Gaulshøj, vp of international at AudienceProject. “Unless we find tactics to deliver relevant ads to the right people, ad blocking will continue to rise toward the levels we’ve seen on desktop.”

“Right now, the common perception in the market is there’s no advertising without tracking,” said von Wersch. “Deactivating tracking in the browser is a de facto ad blocker. That could dramatically increase the ad-blocking problem.”